1. Technical Field
The present invention relates to a key lock and more particularly to a key lock with a removable plug.
2. Background Art
Key locks are used to provide security for many different things, such as desk drawers and electrical switches. Often, unauthorized copies of the keys and/or employee turnover make it desirable to change such locks so that they are operable by different keys.
In order to change the lock in this manner, it is necessary to remove the plug from the lock barrel so that the tumblers in the plug can be changed. Some locks must be completely disassembled from the object (e.g. drawer) being locked in order to do this.
Some other structures have also been provided to permit removal of the plug without disassembly of the entire lock. For example, one known lock has a spring actuated crescent on the plug which engages a groove in the barrel to hold the plug therein. When the plug is rotated to a particular angular position, a wire may be inserted through a hole in the plug to retract the crescent to permit withdrawal of the plug. Insertion of the wire is somewhat difficult and thus makes withdrawal of the plug difficult as well.
Still another structure is shown in U.S. Pat. No. 4,398,405 in which one tumbler is provided at the end of the plug with a retaining end received in a groove in the barrel to prevent removal of the plug. A key (which is longer than the operating key) may be inserted into the plug to move the end tumbler so that its other end projects from the plug and into a longitudinal groove to permit removal of the plug. With this lock, the tumbler which is used to retained the plug in the barrel may be subjected to longitudinal shear forces should someone attempt to remove the plug with an operating key. Since tumblers have a thin longitudinal dimension and are thus not readily adapted to withstand such shear forces, the tumbler retaining the plug in the barrel can be sheared off by a person trying to do so. Further, removal of the plug with this lock requires that a special key be made from a different (i.e. longer) blank than the operating key for the lock. Still further, a person with an operating key and an understanding of this lock could with only a small amount of trial and error have a key made for removal of the plug.
The present invention is directed toward overcoming one or more of the problems above.